Presto Chess: "The first player that gives check with a piece that cannot be taken wins the game."
This leaves it unclear if the checking piece must actually be taken or if it's enough to be able to capture it, and one may instead move the king away or a piece in between. And in the second case: must the capturing move be legal or need it be only pseudolegal?
Another variant of this family:
Like orthodox chess, but a side in check must not move their king. If the check cannot be defended by capturing the checking piece (by a different piece than the king) or moving in between, that side is checkmated and loses. When not in check, one may move the king as usual. Might be called "paralysed king chess".
A milder variant: like above, but the king is allowed to capture a piece attacking him, if it is not a double check.
Presto Chess: "The first player that gives check with a piece that cannot be taken wins the game."
This leaves it unclear if the checking piece must actually be taken or if it's enough to be able to capture it, and one may instead move the king away or a piece in between. And in the second case: must the capturing move be legal or need it be only pseudolegal?
Another variant of this family:
Like orthodox chess, but a side in check must not move their king. If the check cannot be defended by capturing the checking piece (by a different piece than the king) or moving in between, that side is checkmated and loses. When not in check, one may move the king as usual. Might be called "paralysed king chess".
A milder variant: like above, but the king is allowed to capture a piece attacking him, if it is not a double check.